This invention relates to an input member and lever arrangement for use in a brake booster having several modes of actuation including a manual mode, a power assist mode, a combined power assist and manual mode and a traction mode in the development of an output force corresponding to a desired brake application.
In hydraulic brake boosters of a type disclosed in U.S. Pat. Nos. 4,281,585; 4,539,892; 4,625,515; and U.S. application Ser. No. 09/894,106 filed Jun. 28,2001, a control valve is located in a first bore and a power piston is located in a second bore of a housing. A lever arrangement is connected to the power piston and the control valve. An input force applied to a brake pedal by an operator acts on the lever arrangement. The lever arrangement pivots on the power piston and communicates an actuation force that moves the control valve to regulate the flow of pressurize fluid from a source to an operational chamber. The regulated pressurized fluid supplied to the operational chamber acts on the power piston to develop an operational force that pressurizes fluid in the first bore that is supplied to wheel brakes to effect a brake application. A reaction force produced by regulated pressurized fluid in the movement of the power piston is transmitted back to the brake pedal to balance the input force such that the operational force supplied to move the power piston in the first bore is a linear function of the input force applied to the brake pedal.
Additional features such as traction control, dynamic operational control and anti-skid control have been added to hydraulic brake booster to provide a total brake system. However, in such brake systems the brake pedal of the hydraulic booster mirrors the movement of the power piston and as a result have not been incorporated in all vehicles. One way to hold a brake pedal stationary during such additional functions is disclosed by the structure in U.S. Pat. No. 6,203,119 wherein a control valve seat moves while the input member remains in a stationary position to meter operational pressurized fluid from a secondary source to effect a brake application.
A primary object of the present invention is to provide an input member and lever arrangement for a hydraulic brake booster in a brake system wherein the lever arrangement includes a first lever that is retained in a housing of the brake booster by a first pivot pin and joined to a second lever by a second pivot pin to communicate an operational force to a control valve whereby pressurized fluid is metered to a working chamber for the development of an operational force that is proportional to an input force applied to a brake pedal by the input member by an operator and communicated to the lever arrangement for effecting a brake application.
According to this invention, the hydraulic brake booster has a housing with a first bore therein separated from a second bore. The first bore retains the power piston while the second bore retains the control valve. The input member is connected to the power piston and linked to the control valve by a lever arrangement. The input member responds to a brake application force applied to the brake pedal by an operator by communicating a first input force to lever arrangement such that the lever arrangement moves and activates the control valve to meter pressurized fluid to a working chamber in the housing. The pressurized fluid in the working chamber acts on the power piston to develop a hydraulic force for pressurizing fluid in the first bore it is this pressurized fluid that is communicated to wheel brakes in the brake system to effect a corresponding brake application. The input member is characterized by a cylindrical body with a shaft attached thereto. The shaft has a head on a first end that is located in an axial slot bore in the power piston and a second end with threads thereon that are mated with threads in the cylindrical body. A bracket that is located on the shaft and is urged toward the head by a first spring such that a radial opening in the bracket is and remains perpendicular to the shaft. The lever arrangement is characterized by a single first lever with a first end pivotally secured to the housing by a first pin and a second end located in the radial opening of the bracket, and parallel first and second member of second lever with each member having a first end and a second end with the first pin passing through a slot in the first end. A second pin extends through the first and second levers to define a fulcrum point for the lever arrangement. A second spring is located between the power piston and the head of the shaft such that a return spring force is applied to the bracket and communicated through the fulcrum point to bring the first end of the parallel first and second members of the second lever into engagement with the control valve and the second end thereof into engagement with the power piston. The first input force is applied to the second end of the first lever through the engagement of the surface surrounding the radial opening in the bracket causing the second end to first lever to pivot about the first pin and transmit an actuation force through the fulcrum into the second lever. The actuation force acts on the second lever causing the first end of the first and second members to move and activate the control valve whereby metered pressurized fluid is communicated into the working chamber for effecting the brake application. The lever arrangement is characterized in that a first length is defined by a distance between the first pin and the second end on the first lever and a second length is defined by a distance between the first pin and the second end of the first and second members of the second lever. The ratio of the first length to the second length corresponds to a difference in axial movement of the cylindrical body and the power piston and corresponds to proportional relationship of the input force applied to the brake pedal and the hydraulic force produced in the working chamber in effecting a brake application. The lever arrangement is also responsive to a force directly applied to the first end of the first and second members of the second lever to effect a brake application under the control of a ECU to provide to independent braking of a vehicle and reduce the speed of the vehicle to a safe operating level as evaluated by input signals transmitted to the ECU relating to current operating condition of the vehicle.
An advantage of this invention resides in a brake booster having a lever arrangement that directs an input force applied to a brake pedal to actuate a control valve such that the linear movement of a power piston is proportional to an input force applied to effect a brake application.
A further advantage of this invention resides in a lever arrangement whereby a first input force corresponding to an operator brake request or a second input force corresponding to a ECU request is communicated through a lever arrangement to meter pressurized fluid that acts on a power piston to pressurize fluid that is communicated to wheel brakes in a vehicle to effect a brake application.